Dual fuel engines generally run using diesel fuel, gaseous fuel, or both. When an engine is run on gaseous fuel, it is important to maintain the air to fuel ratio to meet emission regulations. The air to fuel ratio of gaseous fuel may be calculated by using the fuel mass flow, which is based on the specific gravity of the gaseous fuel. However, the specific gravity of the gaseous fuel may be unknown.
Current methods for determining the specific gravity of a gaseous fuel include using air and fuel mass quantities. U.S. Pat. No. 7,028,532 (hereinafter “the '532 patent”), assigned to Nissan Motor Co., Ltd., discloses a method for calculating an actual specific gravity of a fuel. It uses a ratio of actual fuel supply weight to the fuel quantity to calculate specific gravity, whereby the fuel quantity is retrieved from a predetermined relationship between fuel quantity, engine speed, and load, and whereby the fuel supply weight is calculated by using an air/fuel ratio and air quantity, both of which are retrieved from tables. Current methods, such as ones described in the '532 patent, require a variety of sensors and relational lookup tables to calculate a specific gravity, each of which may provide a degree of uncertainty.
Thus, a simplified method for determining the specific gravity of a gaseous fuel within a dual fuel system is desired to maintain an air to fuel ratio.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein, nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims.